On a scale where 10/10 is Party of One and 1/10 is Owl's Well that Ends Well:
Return of Harmony part 1: 7/10
Return of Harmony part 2: 8/10
Lesson Zero: 9/10
Luna Eclipsed: 8/10
So, I'm pretty impressed so far. I wouldn't rate these high if I didn't mean it - about half of the season 1 episodes are a 5/10 or worse for me.